LP gas tank with a spark preventer

ABSTRACT

An LP gas tank is adapted to permit it to be safely moved across concrete floors and rocky ground that may contain flint or other hard siliceous material that can generate sparks if struck with a metal, such as steel. The tank is capable of storing the gas under pressure. In addition to a pressure regulator and valve for filling and emptying, the tank also includes a base support. The base support usually is a steel or aluminum base ring. If the tank is dropped on or slid along the floor, it may cause a spark that can trigger a fire or explosion in the presence of gaseous vapors. This problem is solved by either replacing the metal base support with a non-metallic or a non-spark producing metal support, or covering the bottom edge with a suitable non-metallic material, such as an elastomer or a polymer, which will prevent sparking.

FIELD OF THE INVENTION

[0001] The present invention relates to the storing and handling of LP gas. More particularly, it relates to a tank, a cylinder or other pressure vessel in which LP gas can be safely stored and shipped.

BACKGROUND OF THE INVENTION

[0002] LP gas exists as a gas at normal atmospheric pressure and temperature. It is typically stored as a liquid under pressure or at low temperatures. Normally, the gas is stored in a container or tank made entirely of steel or aluminum. The LP gas within the tank is in both a liquid and a gaseous state. When properly handled and used, LP gas is a safe fuel. Characteristics of LP gas include a low flammability point, a high ignition temperature, and immediate vaporization upon exposure to the atmosphere. As the LP gas in its gaseous form is drawn from the tank, it is highly flammable, thereby necessitating precautions as to its use and handling.

[0003] LP gas is a volatile mixture of petroleum hydrocarbons, primarily propane and butane. Its volatility is evidenced by the fact that one volume of liquid LP gas will vaporize into about 250 volumes of vapor. Because of its clean burning characteristics, LP gas has many industrial and domestic uses. In industrial applications, LP gas is used as a basic fuel and as a standby for natural gas. It also finds use as a chemical feedstock and as an aerosol propellant. Domestically, it is used as a fuel for cooking, heating and refrigeration. LP gas is typically shipped and stored in liquid form in pressurized tanks. Many of these tanks are large stationary tanks, tank wagons and tank cars. However, there are untold millions of small portable tanks in use. These can hold from 1 to 40 pounds of gas. The gas is typically transferred from the tank through a fuel hose to meet the requirements of the system that will be using the gas. The fuel hose normally used for LP gas comprises a high-pressure, stainless steel mesh-reinforced neoprene.

[0004] Because of the highly volatile and flammable nature of LP gas, many safety features have been incorporated into the equipment for storing and using the gas. Many of the safety practices associated with LP gas are published in the standards of the National Fire Protection Association as NFPA 58. For example, the standards require the use of a pressure regulator that serves to control the flow of gas to a particular appliance or device that is being fueled.

[0005] Recently, the U.S. Consumer Protection Commission has mandated that all propane tanks sold to consumers must be protected with an overflow protector device. This will serve to reduce a number of fires and explosions caused by over pressurizing the tanks. However, defective and leaky valves, particularly on older tanks equipped with obsolete valves, will continue to be a problem.

[0006] The typical portable LP gas tank includes a pressure regulator and a valve on the top of the tank. The regulator and valve are at least partially surrounded by a protective collar. The regulator is a relief valve that is set to maintain the LP gas as a liquid, but to relieve any pressure that exceeds the tank design limitations.

[0007] At the bottom of the tank is a metal flange called a base ring welded or otherwise secured to the tank. This base ring is generally cylindrical in shape and provides an integral support on which the tank rests in an upright position when the tank is not being lifted or slid from one place to another. When the tank is set down or slid along the floor or the ground, frictional contact between the metal ring and the floor or ground surface can cause sparking to occur. This is particularly true if the floor is concrete or the ground is rocky, and the concrete or the stones contain flint or other fine grained, irregularly shaped siliceous rock or other material that can generate a spark when struck with metal. If this event is coupled with any kind of a leak from the pressurized tank, all of the elements of a fire or explosion, namely a fuel source, a supply of oxygen and an igniter, are present and such an event may occur with devastating effect.

SUMMARY OF THE INVENTION

[0008] Recognizing that a disastrous event can occur when the metal ring or support of an LP gas tank strikes a sharp object capable of sparking, it is an object of the present invention to provide a tank base ring or base support that is equipped with a spark arrester or spark preventer.

[0009] Another object is to economically, yet effectively, modify LP gas tanks to increase the safety of the tanks when they are being moved from place to place.

[0010] These and other objects that will become apparent from the description and drawings that follow are accomplished in the following manner.

[0011] This invention relates to a modification that simply and effectively reduces or eliminates fires and explosions caused by the occurrence of incidental sparks around tanks in which LP gas is stored. Accordingly, the metal base ring or other base support for an LP gas tank is covered, in whole or in part, with a suitable insulation to separate the ring from the floor or ground and to prevent sparking. In this manner, the possibility of a spark occurring, and the possibility of a fire or explosion in the presence of LP gas vapors, is dramatically reduced or eliminated, thereby greatly increasing the safety associated with the handling of LP gas tanks.

[0012] The invention comprises a pressure tank adapted to hold LP gas, the tank having a top including at least one valve for filling or emptying the tank, and a bottom including a base on which the tank is supported. A spark arrester is included in the base. The base support may comprise a base ring, or may comprises at least three legs upon which the tank rests, each leg incorporating or utilizing a spark arrester. The base support normally comprises a material, such as steel, capable of producing a spark upon impact with a hard siliceous material, and is the least partially covered with the spark arresting composition. This composition can be an elastomer, a polymer, or a blend of the two. The elastomer may be a natural rubber or a synthetic rubber, such as butadiene, neoprene or SBR. The polymer may be selected from a number of choices including, but not limited to, Nylon, Delrin, polyurethane or polycarbonate. Still another possibility is to make the spark arrester out of a non-spark inducing metal, such as copper. The spark arrester is attached to the base support by adhesive bonding or by mechanical means. Alternatively, the base support itself may be composed of or fabricated from the spark arresting material.

[0013] The invention also relates to a base support for a tank for LP gas. The base support has at least one edge adapted to contact a surface on which the tank rests, said edge composed, at least in part, of a material that serves as a spark arrester. The base support may be in the shape of a base ring or may comprise at least three support legs. The contact edge may be covered with the spark arrester, or may itself be composed of the spark-arresting composition. The spark-arresting composition is selected from the group consisting of the polymers, elastomers, mixtures thereof, and non-sparking metals.

[0014] The invention also relates to a process for preventing sparking between the bottom edge of a base ring of an LP gas tank and a hard surface. The process comprises the use of a spark-arresting composition along the edge of the base ring. The composition is a polymer, an elastomer, or a mixture thereof. Alternatively, the composition is a non-spark generating metallic material.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is an elevational view showing a traditional portable LP gas tank, equipped with a spark arresting device of the present invention;

[0016]FIG. 2 is an enlarged cross sectional view showing the spark arrester covering a base ring;

[0017]FIG. 3 is a cross section showing a variation of the spark arrester;

[0018]FIG. 4 is a cross section of another variation of the spark arrester;

[0019]FIG. 5 shows yet another variation in cross section; and

[0020]FIG. 6 shows the invention as applied to a different type of tank support.

DETAILED DESCRIPTION OF THE INVENTION

[0021] According to the invention, the base support for an LP gas tank is provided with a spark arrester along its bottom edge so that the edge will not produce a spark when the tank is set on or is dragged across the floor or ground.

[0022] Turning now to the drawings, FIG. 1 is an elevational of view of an LP gas tank of the type that is typically sold to homeowners for cooking on an outdoor grill. The tank 10 comprises a pressurized cylinder 12 containing, for example, 10 pounds of liquid propane. A combination filling and discharge valve and pressure regulator 14 is mounted on top of the tank and is protected from physical damage by a collar or ring 16. The valve 14 is operated by manually turning a handle 18. The cylinder 12 includes a cylindrical base ring 22 that is welded or otherwise secured to the bottom 20 of the cylinder. This provides a cradle in which the tank sets in an upright position. The bottom edge 24 of the ring 22 normally rests on the floor or ground.

[0023] In keeping with the present invention, the bottom base ring 22 of the cylinder 12 has a protective cover 30. This cover prevents sparking when the tank is dropped or set down, or is dragged along a floor or ground. The cover can be secured to the bottom of the ring by any suitable means including, but not limited to, use of an adhesive that is compatible with the composition of the cover and the metal flange. Another option is to use appropriate mechanical fastening means such as rivets, or nuts and bolts, or clips to secure the cover to the ring. Yet another approach is to bond the cover 30 directly to the base ring by, for example, placing the ring in a mold, and injecting an elastomeric or polymeric material into the mold to encapsulate at least the bottom edge of the ring, and then curing the material in situ. By providing several holes in the cylindrical surface of the ring, the elastomer or polymer can be even more securely bonded to the ring.

[0024]FIG. 2 is an enlarged view showing the present invention in greater detail. Here, the protective cover 30 is generally U-shaped in cross section with the bight 30 a covering the contact edge 24 of the base ring 22, and two legs of substantially the same length, an interior leg 30 b and an exterior leg 30 c, extending up, and generally covering the ring 22.

[0025]FIG. 3 shows substantially the same configuration as FIG. 2, with a U-shaped spark arrester 30 having an exterior leg 30 c extending around the outside of the base ring 22 to the top of the ring, and an interior leg 30 b that only extends part way up the inside of the ring 22. Alternatively, the interior leg 30 b may be shortened, or eliminated entirely, with the bight extending radially inwardly a small distance of about one-fourth inch beyond the interior of the contact edge 24 of the base ring 22.

[0026] As shown in FIG. 4, the cover 30 can be shaped so that the interior leg 30 b extends up the inside of the base ring 22 to the top of the ring. As noted, the bight 30 a terminates just a short distance, for example, about one-fourth inch, radially beyond the outer radius of the base ring 22. However, the spark arrester can also include a short exterior leg extending upwardly on the exterior of the ring 22.

[0027] The spark arrester shown in FIGS. 2-4 is typically bonded to the base ring by suitable means, such as a compression fit, or a suitable adhesive. Another alternative is seen in FIG. 5 that shows the spark arrester 30 including an integral spring or saw-tooth clip 32 that permits the arrester to slip onto a base ring 22 but then resists removal of the arrester from the ring. This configuration eliminates the need to adhesively bond the spark arrester to the base ring, and can facilitate the field installation of the spark arrester onto existing portable LP gas tanks.

[0028] Not all portable LP gas tanks will have a base ring as previously described. FIG. 6 shows a base support for a propane tank 12 comprising three legs 44 that are joined to the tank 12 to form a cradle 42 for the tank. The cradle 42 is typically made of the same metal as the tank and is welded to the bottom of the tank. As is shown, each of the legs 44 has a bottom edge 46 and includes a protective cover 30 that serves as a spark arrester. The cover 30 must include at least the bottom of the legs, but can cover the sides as well. Obviously, more than three legs can be used, each one of which has a protective cover on the bottom edge to prevent sparking.

[0029] The cover material comprises a substance that will provide a protective layer between the bottom edge of the base ring and the surface on which the ring is likely to be set, dropped or dragged. Ideally, the material should wear well and should resist abrasion and impact. At the same time, the cover material must be capable of preventing the creation of a spark when the cover is struck against concrete, rocks or other surfaces that may contain small particles of flint or other hard siliceous material that is likely to generate sparks when struck with the steel or aluminum ring. Finally, material must be capable of being secured or bonded to the base ring.

[0030] Examples of material that may be used as a protective insulator or cover are thermoplastic or thermosetting polymers, such as Nylon, Delrin, polyurethanes, acrylics, epoxies, phenolics, polyesters, PVC and polycarbonates. Various elastomers, such as natural and synthetic rubber, including butadiene, neoprene and SBR in combination with other elastomers and polymers may likewise be used. The material should have sufficient impact strength so that it will not fracture or shatter upon impact. Furthermore, the material typically includes antioxidants, UV protectors, plasticizers and other additives for rendering such compositions useful as insulating covers.

[0031] The thickness of the material covering the base ring or the support legs can range from about one-eighth inch to about one-fourth inch depending on the durometer or hardness of the material and its scuff and wear resistance.

[0032] It should be understood that the objectives of the present invention can be achieved by other means as well as those articulated without departing from the scope and intent of the present invention. For example, the metal base ring can be replaced by a rigid or semi-rigid polymeric or elastomeric ring that is secured to the bottom of the tank by a suitable bonding agent, such as an epoxy or a cyanao-acrylate cement, or by curing the ring in situ with or without a catalyst. Also, the invention is useful in connection with any tank support that is or can be used for LP gas containers.

[0033] While the invention has been described in combination with embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing teachings. Accordingly, the invention is intended to embrace all such alternatives, modifications and variations as fall within the spirit and scope of the appended claims. 

What is claimed is:
 1. A pressure tank adapted to hold LP gas, the tank having a top including at least one valve for filling or emptying the tank, and a bottom, said bottom including a base on which the tank is supported, the improvement comprising a spark arrester included in the base.
 2. The tank according to claim 1 wherein the base comprises a base ring.
 3. The tank according to claim 2 wherein the base ring normally comprises a material capable of producing a spark upon striking a hard surface, and is the least partially covered with the spark arresting composition.
 4. The tank according to claim 3 wherein the spark-arresting composition is an elastomer, a polymer, or a combination of the two.
 5. The tank according to claim 4 wherein the spark-arresting composition is attached to the base ring by adhesive bonding or by mechanical means.
 6. The tank according to claim 4 wherein the spark-arresting composition is an elastomer selected from the group consisting of natural rubber and synthetic rubber.
 7. The tank according to claim 1 wherein the base is composed of a spark-arresting material.
 8. The tank according to claim 1 wherein the base comprises at least three legs, each of which includes a spark arrester.
 9. A base support for a tank for LP gas, the base support having at least one edge adapted to contact a surface on which the tank rests, said edge composed, at least in part, of a composition that serves as a spark arrester.
 10. The base support according to claim 9, said support having the shape of a base ring having a surface contact edge.
 11. The base support according claim 10 wherein the surface contact edge is covered by the spark arrester composition.
 12. The base support according to claim 10 wherein the base ring is composed of a spark-arresting composition.
 13. The base support according to claim 9 wherein the spark arrester composition is selected from the group consisting of the polymers, elastomers, and mixtures thereof.
 14. The process for preventing sparking between the bottom edge of a support for an LP gas tank and a hard surface, comprising the use of a spark-arresting composition along the bottom edge of the support.
 15. The process according to claim 14 wherein the spark-arresting composition is selected from the group consisting of polymers, elastomers, and mixtures thereof.
 16. The process according to claim 14 wherein the composition comprises a non-spark producing metal.
 17. The process according to claim 14 wherein the support is a base ring.
 18. The process according to claim 14 wherein the support comprises at least three legs on which the tank rests. 